In interactive numerical control devices, programming is effected in such a way that queries on various items requiring data are systematically made by the system, and an operator inputs required values in answer to the queries. Accordingly, the operator can create programs without the need to comply with language rules for automatic programming or an NC tape format.
Programs produced in this manner must be checked for errors, and in interactive numerical control devices, the checking is executed by using a check drawing function. Namely, a simulation is carried out wherein profiles such as the shapes of a material and a tool are drawn on a display screen and the tool is moved along a path instructed by the NC program so that the workpiece is progressively machined into a desired shape.
As techniques for drawing a three-dimensional shape, a solid drawing method and a wire frame drawing method are known. According to the solid drawing method, a complicated profile of a solid body is represented by outer surfaces enclosing the body, the various types of surfaces being enclosed by ridgelines. The wire frame drawing method uses figure elements such as a straight line, a second degree curve, and a spline curve, etc., and a three-dimensional shape is represented solely by the lines of these elements.
According to the solid drawing method, since the drawn profile consists of surfaces, it is easy to recognize an actual machining profile, and when a workpiece is machined, the process can be easily followed because the surfaces are cut away. It is, however, difficult to draw a tool path and a detailed profile to be machined, and since the objects are represented by surfaces, a vast quantity of complicated data must be processed, requiring much time for the drawing. Moreover, a problem arises in that colors become blurred when small parts are drawn.
The wire frame drawing method is better, in that it can draw a tool path and a detailed profile to be machined, but since objects are represented solely by lines, it is difficult to recognize the drawn workpiece as a solid body.
Therefore, although each of the above two drawing methods compensates for the shortcomings of the other, conventionally the solid drawing method and the wire frame drawing method are used independently as different drawing methods.